Images acquired by an optical camera experience a vignetting effect. The vignetting effect can yield non-uniform intensity in an image. For example, a periphery of an image may be darker than a center of an image. One cause of vignetting is that an amount of light projected through camera optics decreases with an angle of incidence against the optical axis. Another cause of vignetting is asymmetries in optics. The intensity of vignetting effects increases as lenses get smaller. Therefore, cameras in handheld electronic devices (e.g., cellular telephones) can experience significant vignetting. For example, the periphery of an image acquired by a cellular telephone camera may be 500% less bright than the center of the image.
Cameras account for vignetting by performing spatial falloff corrections. A falloff correction unit (FCU) applies a gain value to each pixel to produce a desired (e.g., uniform) brightness across an image. One conventional FCU stores in memory a gain value for each possible pixel location in an image that can be captured by a camera housing the FCU. As image sizes grow the memory required to support this conventional style FCU may become unsupportable and/or not cost effective in mobile devices. Another conventional FCU does not store any gain values but rather computes a gain value for each pixel in an image using a radial falloff computation. The radial falloff computation determines a gain value as a function of the distance of a pixel from the center of an image. This approach suffers when falloff characteristics are not uniform. Another conventional FCU also does not store any gain values but rather computes a gain value for each pixel in an image according to a general characterization equation. General characterization equations may be complex and thus computationally expensive to solve. One skilled in the art will appreciate that information included in the background section is not admitted prior art.